The present invention relates to a thin film formation technology suitable for manufacturing a display and a color filter having an EL (electroluminescence) device or an LED (light emitting diode), and more particularly to a technology advantageous for forming a multi-layer thin film layer between partition elements.
An ink jet method has been used to fill material, such as color resin, to organic semiconductor film of a display or to a color filter to manufacture liquid crystal panels for color display.
When material is filled by an ink jet method, it is necessary to form partition elements to partition pixel areas (hereafter also calledxe2x80x9cbanksxe2x80x9d, a layer to form partition elements is called a xe2x80x9cbank layerxe2x80x9d), and to fill a thin film material solution to the area enclosed with the partition elements. A thin film material solution, which volume is much larger than the volume after film formation, is filled in the pixel area enclosed with the partition elements. Since a display is generally demanded to be slim, the height of the partition elements is limited. Therefore the behavior of the thin film material solution filled there differs depending on the wettability (affinity) which the partition elements and the area enclosed with the partition elements have for the thin film material solution.
If the partition elements have affinity for the material, the material easily flows over to the adjacent pixel areas, even if the partition elements exist, when an amount of material exceeding the height of the partition elements is filled, as shown in FIG. 9A. If the partition elements have no affinity for the material, the material does not flow over to the adjacent pixel areas due to the surface tension of the material, even if the amount of material exceeding the height of the partition materials is filled, as shown in FIG. 9B. If this material is heated to evaporate the solvent, thickness after film formation becomes thick at the center of the pixel area and thin at the edges, since the material is repelled by the side walls of the partition elements, as shown in FIG. 9C. This causes color unevenness and reduces reliability. Also if the partition elements are comprised of non-affinity elements, adhesion of the partition elements and ground plane of the partition elements is weak, which makes partition elements easily separate.
A prior art to solve such problems is a surface treatment technology to make the top of the partition elements have no affinity and to make the other portions have affinity. Japanese Patent Laid-open No. 9-203803 and Japanese Patent Laid-open No. 9-230129, for example, disclose a technology to process the top portion of the partition elements to be ink repellent by irradiating ultraviolet rays, and the area enclosed with the partition elements to have affinity for ink. For the former, an ink repellent (non-affinity) layer is coated at the top portion of the partition elements, and for the latter, the concave portion enclosed with the partition elements is made to have affinity for ink (affinity) by ultraviolet irradiation. Logical considerations of this technology are written in International Display Research Conference 1997, pp. 238-241. According to this technology, even if material is filled to the height exceeding the height of the partition elements, the material is repelled by the non-affinity film, and does not overflow to the adjacent pixel areas, as shown in FIG. 10 A, since the side walls of the partition elements have affinity, and the thickness of formed film does not become thin at the edges of the pixel areas.
However, even in the above known technology, it is not clear how to set affinity of the side walls of the partition elements, therefore it is difficult to obtain a flat thin film layer. Japanese Patent Laid-open No. 9-230129 states that the degree of affinity is controlled by irradiating ultraviolet rays from both the front and back sides, but the degree of affinity and non-affinity, that is, how to set the respective contact angle to the thin film material solution, is not known.
If the non-affinity is too high, for example, the thin film layer becomes thin at the edges near the partition elements and thick at the center as shown in FIG. 9C. If affinity is too high, on the other hand, the thin film layer becomes thick at the edges near the partition elements and thin at the center as shown in FIG. 10B.
Also the above known technology assumes that there is only one thin film layer, therefore it is totally unknown how to treat the surface for forming a flat thin film layer for each layer when multi-layered thin film layers are formed. If the above known technology is applied for each layer, surface treatment is required each time a layer is formed, which requires numerous processing steps.
The present inventor discovered that if plasma treatment is performed using fluorine gas, the contact angle to ink is greatly different between an organic substance and an inorganic substance, depending on the mixing ratio of oxygen gas and fluorine gas. The present inventor also discovered that affinity can be controlled by forming banks where affinity material and non-affinity material are alternately layered and by executing plasma treatment.
It is accordingly a first object of the present invention to provide a thin film formation method which allows the formation of multi-layer thin films by laminating a bank using different materials.
A second object of the present invention is to control affinity without going through many processing steps for affinity control by managing surface treatment under predetermined conditions, so as to decrease the cost required for affinity control and to form multi-layer thin films having a uniform film thickness.
A third object of the present invention is to provide a display layered by the thin film formation method which can form multi-layer films. By this, image display without uneven brightness and color is implemented and reliability is improved.
A fourth object of the present invention is to provide a color filter layered by the thin film formation method which can form multi-layer films. By this, image display without uneven brightness and color is implemented.
To achieve the first object, the present invention is a thin film formation method for forming a thin film layer by filling a thin film material solution in areas enclosed with banks, comprising a step of forming the banks on a bank formation face, and a step of filling the thin film material solution in the banks. The step of forming the banks is for forming the banks where an affinity bank layer and a non-affinity bank layer are alternately layered by repeating the step of forming the affinity bank layer with an affinity material and a step of forming the non-affinity bank layer with a non-affinity material one or more times.
xe2x80x9cBanksxe2x80x9d here refer to partition elements which are formed to partition pixels of a display using a non-affinity semiconductor thin film device or to partition pixel areas of a color filter. For the layer structure of a bank, the type of non-affinity material or affinity material may be changed for each layer. The thickness of each layer to be layered may be changed for each layer. The bank formation face is a face where the banks are formed, and may be a drive board of a display or a transparent board of a color filter.
Affinity or non-affinity here is determined depending on the characteristics of the thin film material solution used to fill. If the thin film material solution has a hydrophilic property, for example, the surface having a polar group exhibits affinity, and the surface having a non-polar group exhibits non-affinity. If the thin film material solution has a lipophilic property, on the other hand, the surface having a polar group exhibits non-affinity, and the surface having a non-polar group exhibits affinity. The thin film material solution is selected in various ways depending on the manufacturing target. When the hydrophilic property or hydrophobic property of the thin film material solution changes at every layer, the layer structure is changed such that the bottom layer, of the two bank layers formed at positions corresponding to the thin film layer formed by the thin film material solution, exhibits non-affinity to the thin film material solution, and the top layer exhibits affinity. When the thin film material solution has a hydrophilic property, for example, an affinity material is an inorganic material and a non-affinity material is an organic material. When the thin film material solution has a hydrophobic property, an affinity material is an organic material and a non-affinity material is an inorganic material.
This involves, for example, a method for forming the above mentioned bank layer by coating materials. In other words, the step of forming the non-affinity bank layer and the step of forming the affinity bank layer are steps of forming respective bank layers by coating predetermined materials dissolved in solvent. And the non-affinity bank layer is formed by coating the material for the non-affinity bank layer before removing the solvent where the material of the affinity bank layer is dissolved.
To achieve the second object, the present invention further comprises a step of executing a predetermined surface treatment for the banks and bank formation faces after the above step of forming the banks. For the surface treatment, reduced pressure plasma treatment or atmospheric pressure plasma treatment is performed where the plasma gas is irradiated under a reduced pressure atmosphere or under atmospheric pressure using gas containing a fluorine or fluorine compound as the introductory gas. A prescribed condition is, for example, to execute plasma treatment in gas containing a fluorine compound and oxygen. Under this condition, a non-reactive group is generated on the surface of the inorganic material by plasma discharge, the non-reactive group is oxidized by oxygen, and a polar group, such as a carbonyl group or hydroxyl group, is generated. The polar group exhibits an affinity for fluid containing polar molecules, such as water, and exhibits non-affinity for fluid containing non-polar molecules. In parallel with the above reaction, a phenomenon where the fluorine compound molecules enter the organic material surface also occurs on the surface of the organic bank layer.
Particularly when the amount of fluorine compound is more than oxygen, that is, when the content of the fluorine compound to the total amount of fluorine compound and oxygen is set to 60% or more, for example, the surface is non-polarized by the mixing phenomenon of fluorine compound rather than by the influence of oxidation, since the mixing phenomenon of fluorine compound is more active than oxidation by oxygen in a gas atmosphere where the amount of fluorine compound exceeds oxygen. Therefore if plasma treatment is executed for an organic material under the condition where the amount of fluorine compound exceeds oxygen, the organic material exhibits a non-affinity for fluid containing polar molecules and exhibits an affinity for fluid containing non-polar molecules. For the gas containing fluorine, halogen gas, such as CF4, SF6 or CHF3, is used. If a surface treatment is executed under this condition, the affinity of the surface of the non-affinity bank layer and the affinity bank layer is adjusted such that the difference between respective contact angles to the thin film material solution is greater. As a result, the surface is treated such that the contact angle of the surface of the affinity bank layer to the thin film material solution becomes 30 degrees or less, for example. And the surface is treated such that the contact angle of the non-affinity bank layer to the thin film material solution becomes 40 degrees or more, for example.
In the above mentioned surface treatment step, the surface treatment is executed under a predetermined condition where the non-affinity bank layer has a higher degree of non-affinity for the thin film material solution compared with the affinity material. Also in the surface treatment step., the surface treatment is executed under a predetermined condition where the affinity of the affinity bank layer for the thin film material solution is less than the affinity of the area enclosed with the banks for the thin film material solution.
In the above mentioned step of forming the banks, a set of an affinity bank layer and a non-affinity bank layer is formed by, for example, an affinity bank layer formation step of forming the affinity film with an affinity material, a non-affinity bank layer formation step of forming the non-affinity bank layer with a non-affinity material matching the bank formation area on the affinity bank layer, and a removal step of removing the affinity bank layer at the area where the non-affinity bank layer is not formed by etching using the non-affinity bank layer as a mask. Also in the step of forming the banks, a set of a affinity bank layer and a non-affinity bank layer is formed by a step of forming the affinity bank layer with an affinity material, a step of etching for etching the affinity bank layer matching the bank formation area in the bottom layer, a step of forming the non-affinity bank layer with a non-affinity material covering the affinity bank layer, and a step of etching the non-affinity bank layer matching the bank formation area in the top layer. It is also acceptable to collectively etch two or more sets of an affinity bank layer and a non-affinity, bank layer after overlaying all or most of the affinity bank layers and non-affinity bank layers, rather than to perform etching to form a bank shape each time.
Here the non-affinity material is, for example, polyimide, amorphous silicon, polysilicon, an organic compound containing fluorine or an insulating organic compound (photosensitive material). The affinity material is such metal as Al and Ta, silicon oxide film or silicon nitride film.
Preferably in the thin film layers, the thin film layer at the lowest layer is set to roughly the same thickness as the affinity bank layer at the lowest layer of the bank. And each thin film layer layered on the lowest layer is set to a thickness roughly the same as the total of the respective thicknesses of the affinity bank layer and the non-affinity bank layer which are layered to a height corresponding to the banks. The contact shape of the wall faces of the banks and the liquid surface of the filled thin film material solution changes depending on the affinity of the wall faces. In the contact face with the affinity bank layer, the thickness of the thin film tends to increase since the thin film material solution contacts the wall face, and in the contact face with the non-affinity bank layer, the thickness of the thin film tends to decrease since the thin film material solution is repelled. The large amount of thin film material solution, which is filled, gradually decreases its volume by a heat treatment and other reasons, but if the layered structure is adjusted such that the liquid level of the thin film material solution comes to the boundary between the non-affinity bank layer and the affinity bank layer after heat treatment, then the characteristics of the non-affinity bank layer and the affinity bank layer are balanced, and the liquid level of the thin film material solution becomes vertical to the bank wall face, generally becoming flat. For example, the thickness of the non-affinity bank layer at the top layer is set to 500 nm or less, and the thickness of the other non-affinity bank layer is set to 100 nm or less.
To achieve the third object, the present invention is a display comprised of layered thin film layer formed by filling thin film material solution in an area enclosed with banks, characterized in that the bank is comprised of alternately layered affinity bank layers formed with a material having affinity for the above mentioned thin film material solution and non-affinity bank layers formed with a material having non-affinity for the above mentioned thin film material solution, pixel electrodes made of ITO, for example, are formed in the area enclosed with the above mentioned banks, and the above mentioned thin film layer is formed with an organic semiconductor material for forming a thin film light emitting element.
To achieve the fourth object, the present invention is a color filter comprised of layered thin film layers formed by filling a thin film material solution in areas enclosed with banks, characterized in that the bank is comprised of alternately layered affinity bank layers formed with a material having affinity for the above mentioned thin film material solution and non-affinity bank layers formed with a material having non-affinity for the above mentioned thin film material solution, a bank formation face is formed as a transparent board, the above mentioned banks are partition elements for partitioning the pixel areas, and the above mentioned thin film layer is formed with a color resin material for providing colors to the above mentioned pixels.
In the above mentioned display and color filter, the affinity bank layer and/or the non-affinity bank layer are surface-treated so as to have affinity or non-affinity respectively.